The term "neurosurgery" generally conjures up images of invasive surgery to remove brain tumors, to repair arteries or veins in the neck and brain, or to treat spinal cord trauma. The rapidly growing subspecialty of functional neurosurgery, however, employs a variety of minimally invasive procedures to treat a wide range of neurological disorders.

"It's called 'functional neurosurgery' because we alter the function of the brain," says Dr. Sandeep Kunwar, a neurosurgeon at Washington Hospital. "These techniques can have an impressive impact on the quality of life for patients whose conditions have not responded to medications or other therapies."

According to the American Association of Neurological Surgeons (AANS), which is highlighting functional neurosurgery in August during Neurosurgery Outreach Month, millions of people in the U.S. are affected by conditions that may be treated through these procedures:* An estimated 1.5 million Americans have Parkinson's disease, with 60,000 new cases being diagnosed each year.* Essential tremor - a nerve disorder characterized by uncontrolled shaking of the hands or sometimes other body parts - affects about 5 million people in the United States.* Severe psychiatric illness, including chronic depression and obsessive-compulsive disorder, affects an estimated 18 million Americans.* An estimated one in five people suffer moderate to severe chronic pain that may dramatically impact their lifestyle.* Approximately 2.5 million Americans have epilepsy, and as many as 9 percent of people may experience a seizure at some point in their lives.

"One procedure that neurosurgeons are in the process of developing is called deep brain stimulation, or DBS," Dr. Kunwar says. "It has been used for many years to treat intractable pain, but now neurosurgeons use it to treat Parkinson's patients who have not responded to medical therapy. It's a minimally invasive procedure in which an electrode is inserted into the head and then connected to a tiny pacemaker-like device inserted in the chest wall. The device sends continuous electrical impulses to the target area in the brain to alleviate the patient's symptoms and improve the quality of life."

DBS also is sometimes used to treat essential tremor and for involuntary movements associated with disorders such as multiple sclerosis. "DBS also is being tested in clinical trials for treating obsessive-compulsive disorder and major depression," he says.

Another advance in the treatment of essential tremor that hasn't responded to beta blockers or other medications is to disrupt the function of the thalamic portion of the brain using gamma knife surgery.

"Gamma knife surgery doesn't entail any incisions," Dr. Kunwar explains. "Instead, it uses highly focused beams of radiation to reach into the brain. It's an outpatient procedure, and the tremors usually resolve within four to eight weeks. The efficacy is usually greater than 90 percent."

Gamma knife surgery is also a procedure being used to treat a facial pain syndrome called trigeminal neuralgia. "People who have this condition describe it as the worst pain they have ever felt," Dr. Kunwar says. "In some cases, we might perform a fairly major surgery called microvascular decompression to remove the blood vessel that's rubbing against the nerve. More than 90 percent of patients are pain-free right after the surgery, but it entails using general anesthesia and staying several days in the hospital.

"Gamma knife surgery to deaden the nerve doesn't carry the risks of anesthesia and is done on an outpatient basis," he continues. "It has similar efficacy - with 85 percent of patients being free of pain after one or two months following treatment and is a very safe procedure that often enables patients to quit taking pain medications on a daily basis."

Dr. Kunwar notes that gamma knife surgery is currently being used in Europe to target portions of the brain's temporal lobe to control epileptic seizures. "This technique is now in clinical trials in the U.S.," he says. "The procedure is very promising, with many patients becoming seizure-free within six to 12 months, but it may take several years for approval by the FDA for general use in the U.S."

In the meantime, American neurosurgeons can perform surgical temporal lobectomy to treat seizures that don't respond to medications. "This surgery is quite effective in controlling epileptic seizures, but it is quite extensive and requires a lengthy hospital stay," Dr. Kunwar says.

"Another option is a minimally invasive procedure called vagus nerve stimulation - or VNS - that is similar to DBS," he adds. We insert an electrode next to the vagus nerve in the neck and the pacemaker-like device in the chest wall. VNS helps decrease the frequency of seizures by about 50 percent in about 50 percent of patients. It is not ideal, but it still may make a substantial difference in the patient's quality of life."